The present invention relates to the methods of obtaining the adjustable capacitor for low-voltage and high-voltage.
U.S. Pat. No. 3,569,795, C1.317/231 of Gikow is an example of well known voltage variable capacitors of alternating current in which a capacity of a capacitor is changed as a result of the effect of changing a dielectric constant of a ferroelectric material by direct current control voltage. The capacitors of this type have relatively narrow range of changing a capacity and the used principle of changing a capacity cannot transform other types of capacitors into variable capacitors.
Gikow in U.S. Pat. No. 3,562,637, C1.323/74, uses direct current control voltage, applied to each capacitor from a plurality of capacitors (at least four capacitors), for obtaining the adjustable capacitor of alternating current. The control voltage creates on each of the pairs of said capacitors, connected together in series, voltages which have opposite directions and counteract each other. In this technical solution all energy of charging of said serially connected capacitors cannot be discharged and the energy, which cannot be discharged, is approximately proportional to (CU.sub.c).sup.2 where U.sub.c is the control voltage, C is the capacitance of one of said capacitors. The mentioned shortcomings decrease the range of changing the capacity. Said plurality of capacitors cannot provide a rapid extraction of the stored energy into a load because voltages on each of the pairs of said capacitors have opposite directions and the electric changes on each of two connected together plates of said capacitors are the same: positive or negative. For obtaining the adjustable capacitors according to both Gikow U.S. Pat. No. 3,562,637 and 3,569,795, it is necessary to use a source of control voltage of direct current with resistors and to recuperate relatively high energy losses on said resistors.
In U.S. Pat. No. 5,600,187, C1.307/157, El-Hamamsy et al (for obtaining the adjustable capacitor of alternating current) use direct current bias voltage V.sub.ds applied to drain and source terminals of a MOSFET, having a body diode integral therewith, whose gate and source terminals are connected together, where said MOSFET is connected in series with a capacitor C.sub.1 and the voltage of operating electric circuit of alternating current is applied to said serially connected MOSFET and capacitor. The output capacitance of said MOSFET comprises the sum of its drain-to-source capacitance and its drain-to-gate capacitance. According to El-Hamamsy et al, both of these interelectrode capacitances vary with the voltage of direct current V.sub.ds applied to drain and source terminals of said MOSFET. As said voltage V.sub.ds increases, the interelectrode capacitances decrease, thus decreasing the total capacitance between terminals. In this Patent the capacitor C.sub.1 is utilized as a protective device which prevents significant power losses. For obtaining a variable capacitor El-Hamamsy et al. use the conception of changing drain-to-source capacitance and drain-to-gate capacitance of a MOSFET by changing said voltage V.sub.ds of direct current. This conception has the following shortcomings:
It has very narrow industrial applicability and according to El-Hamamsy et al, the technical solutions of U.S. Pat. No. 5,600,187 are useful as a tuning capacitor in an electrodeless HID lamp ballast;
The peak of energy density is not high;
It can only be utilized for obtaining a variable capacitor of picofarad values;
It cannot be utilized for obtaining a variable Electrolytic Capacitor, etc.
Examples of switching capacitor without moving parts are described in U.S. Pat. Nos. 3,778,645, C1.307/318. This invention includes the steps of; connecting a tunneling capacitor in series with in parallel connected an invariable resistor and a second capacitor; applying a bias impulse voltage to said capacitors. As a result of applying a bias voltage to said capacitors, the tunneling current of the tunneling capacitor increases exponentially and capacitance is changed from a first value to a second value. An impulse direct current voltage source is utilized for applying said bias impulse voltage, Technical solutions of U.S. Pat. No. 3,778,645 do not include a switching device connected to said tunneling capacitor. The equivalent circuit is presented with a switching device SW.sub.2 (FIG.3) for explaining creation of a tunneling current by said tunneling capacitor and by said applied bias voltage. In U.S. Pat. No. 3,778,645, one cannot find the following information: is said tunneling capacitor larger or smaller in comparison with said second capacitor?; is said resistor connected in parallel with larger or smaller of said capacitors? This U.S. Patent includes technical solutions with two tunneling sections which are placed in series with oppositely poled unidirectional devices, This method has the following shortcomings:
The impulse direct current voltage source affects the value and the form of operating alternating voltage when applying the bias voltage;
It cannot provide a rapid extraction of all stored energy into a load, in an operating circuit of direct current;
Used principle of changing a capacity cannot smoothly change a capacitance and cannot transform other types of capacitors into variable capacitors;
The tunneling current increases energy losses. It is also necessary to underline that the technical solutions, presented in U.S. Pat. No. 3,778,645, can only function with said tunneling capacitor whose structure is described in the claims 2, 3 and 7 of said Patent.
A conception, which permits transforming all types of invariable capacitors into adjustable capacitors and simultaneously obtaining a voltage source with stepless voltage control, does not exist in the art.
It exists only one practically useful method for smooth control of a rate of charge of all types of capacitors in an operating electric circuit. This method includes the step of charging a capacitor through a variable current limiting device and changing a rate of charge of said capacitor by changing an impedance of said current limiting device. Therefore, said variable current limiting device must have a design voltage no less than the voltage of said operating electric circuit and a design power which is proportional to I.sup.2, where I is an average current of charging of said capacitor.